National Instruments SCXI-1141 Manual

CALIBRATION PROCEDURE
SCXI -1141/1142/1143
This document contains the information and instructions needed to
calibrate the SCXI-1141/1142/1143 using Traditional NI-DAQ (Legacy).
Calibrate the SCXI-1141/1142/1143 at a regular interval as defined by the
measurement accuracy requirements of your application. NI recommends
performing a complete calibration at least once every year. Based on your
measurement accuracy needs, you can shorten this interval to 90 days or
six months.
Conventions
The following conventions apply to this document:
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hot. Touching this component may result in bodily injury.
bold Bold text denotes items that you must select or click in the software, such
as menu items and dialog box options. Bold text also denotes parameter
names.
™

SCXI-1141/1142/1143 Calibration Procedure 2 ni.com
italic Italic text denotes variables, emphasis, a cross-reference, or an introduction
to a key concept. Italic text also denotes text that is a placeholder for a word
or value that you must supply.
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programs, subprograms, subroutines, device names, functions, operations,
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Software
Calibration requires the latest version of Traditional NI-DAQ (Legacy),
which includes high-level function calls to simplify the task of writing
software to calibrate devices. Traditional NI-DAQ (Legacy) supports many
programming languages, including LabVIEW, LabWindows™/CVI™,
Microsoft Visual C++, Microsoft Visual Basic, and Borland C++.
If the SCXI-1141/1142/1143 is revision F or later, this procedure requires
using a calibration software library. The library contains a function that is
needed to adjust calibration circuitry on the module. If you do not have the
software library files, you can download them from ni.com/info, using
info code exgpxj.
The calibration software library consists of these files:
•SCXIdpCal.dll
•SCXIdpCal.h
Note Determine the revision of the SCXI-1141/1142/1143 by checking the part number
of the module, which is located on the outside of the module case. For example, part
number 182628C-01 is revision C.

©National Instruments Corporation 3 SCXI-1141/1142/1143 Calibration Procedure
Documentation
The following documents are the primary references for writing your
calibration utility:
• The Traditional NI-DAQ Function Reference Help includes
information about the functions in Traditional NI-DAQ (Legacy).
• The DAQ Getting Started Guide provides instructions for installing
and configuring NI-DAQ devices.
• The SCXI Quick Start Guide includes information for installing and
configuring the SCXI chassis.
• The Traditional NI-DAQ User Manual includes information about
creating applications that use Traditional NI-DAQ (Legacy).
You can add these help files when you install Traditional NI-DAQ
(Legacy). After adding these help files, you can access them by selecting
Start»Programs»National Instruments NI-DAQ»Online-DAQ
Support. The documents provide instructions about installing and
configuring DAQ devices. The documents also include detailed
information about creating applications that use Traditional NI-DAQ
(Legacy). For more information about the SCXI-1141/1142/1143, refer
to the SCXI-1141/1142/1143 User Manual.
Test Equipment
NI recommends using the equipment in Table 1 to verify and calibrate the
SCXI-1141/1142/1143. If these instruments are not available, use the
accuracy requirements listed to select a suitable substitute.
Table 1. Test Equipment
Equipment
Recommended
Model Accuracy
Calibrator Fluke 5700A 50 ppm
DMM NI 4060 5 1/2 digit, 15 ppm
DAQ Device NI 6030E 16-bit minimum
Terminal Block SCXI-1304 N/A

SCXI-1141/1142/1143 Calibration Procedure 4 ni.com
Test Conditions
Follow these guidelines to optimize the connections and the environment
during calibration:
• Keep connections to the SCXI terminal block and the rear connector of
the SCXI module short. Long cables and wires act as antennae, picking
up extra noise and thermal offsets that can affect measurements.
• Use shielded copper wire for all cable connections to the
SCXI-1141/1142/1143. Use twisted-pair wire to reduce noise.
• Maintain the temperature between 18 and 28 °C.
• Keep relative humidity below 80%.
• Allow a warm-up time of at least 15 minutes for the SCXI module and
30 minutes for the DAQ device to ensure the measurement circuitry is
at a stable operating temperature.
Calibration Procedure
This section provides step-by-step instructions for calling the appropriate
calibration functions.
The steps used in the calibration procedure are as follows:
1. Setting up the SCXI-1141/1142/1143 for testing.
2. Verifying the existing operation of the SCXI-1141/1142/1143 to
determine whether it is operating within its test limits.
3. Adjusting the offset and gain errors using a known external voltage
source.
4. Verifying that the SCXI-1141/1142/1143 is operating within its test
limits after adjustments.
Setting up the SCXI-1141/1142/1143 for Calibration
Complete the following steps, while referring to Figure 1 to set up the
SCXI-1141/1142/1143 for calibration.
1. Make sure all components involved in the calibration procedure are
powered-off.
2. Assemble the SCXI-1141/1142/1143, chassis, terminal block, and
DAQ device as shown in Figure 1. The SCXI module you are
calibrating must be connected directly to the DAQ device.
3. Power on the SCXI chassis and the external computer.
4. Make sure that all the appropriate driver and application software is
installed.

©National Instruments Corporation 5 SCXI-1141/1142/1143 Calibration Procedure
5. You must configure the hardware properly with Measurement &
Automation Explorer (MAX) under Traditional NI-DAQ (Legacy).
Refer to the SCXI Quick Start Guide for details about configuring the
SCXI chassis.
Figure 1. Typical SCXI-1141/1142/1143 Setup for Calibration
Verifying the Operation of the SCXI-1141/1142/1143
The verification procedure determines how well the SCXI-1141/1142/1143
is meeting its specifications. You can use this information to select the
appropriate calibration interval for your application.
1 SCXI-1304 Terminal Block
2 SCXI-1141/1142/1143 Module
3 SCXI Chassis
4 SCXI-1349 Cable Adapter
5 Shielded 68-Pin Cable
6 NB1 Cable (50-Pin Ribbon Cable)
7 TBX 50-Pin Terminal Block
8 Cable to DMM
9 Cable to Calibrator
10 Calibrator
11 DMM
12 DAQ Device
®
MAINFRAME
SCXI
5
4
3
2
1
ADDRESS
SCXI1100
2468 10 12 14 16 18 20 20 24 26 28 30 32 34 36 38 40 42 44 46 48 50
13 5 7 911131517 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
3
1
2
4
5
7
8
11
6
9
12
10

SCXI-1141/1142/1143 Calibration Procedure 6 ni.com
Verifying Analog Input Measurements
Complete the following steps to verify the analog input offsets of the
SCXI-1141/1142/1143:
1. Read the Test Conditions section in this document.
2. Refer to Table 9 for the specifications to test. Table 9 shows all
acceptable settings for the module. NI recommends that you verify all
ranges and gains. However, you can save time by checking only the
ranges that your application uses.
3. Ensure that the E Series DAQ device is connected to the SCXI module.
4. Call Calibrate_E_Series to minimize any uncertainty associated
with the E Series DAQ device. Set the following parameters:
•device—The Traditional NI-DAQ (Legacy) device number
assigned by MAX
•calOp—ND_SELF_CALIBRATE
•setOfCalConst—ND_USER_EEPROM_AREA
•calRefVolts—0.0
5. Call MIO_Config to enable dithering on the E Series DAQ device
measurements. Set the following parameters:
•DAQdeviceNumber—The Traditional NI-DAQ (Legacy) device
number assigned by MAX
•dither—1
•useAMUX—0
6. Call SCXI_Single_Chan_Setup to configure the module for
single-channel measurements. Set the following parameters:
•SCXIchassisID—The chassis ID value obtained from MAX
•moduleSlot—1
•moduleChan—0
•DAQdeviceNumber—The cabled device number assigned by
MAX to the E Series DAQ device
7. Call SCXI_Set_Gain to configure the module to the gain value you
want to test. Set the following parameters:
•SCXIchassisID—The value obtained from MAX
•moduleSlot—1
•moduleChan—0
•gain—The gain value from Table 9 that you want to test
8. Call SCXI_Configure_Filter to disable the filter.
Set the following parameters:
•SCXIchassisID—The value obtained from MAX

©National Instruments Corporation 7 SCXI-1141/1142/1143 Calibration Procedure
•moduleSlot—1
•channel—0
•filterMode—0
•freq—0 kHz
•cutoffDivDown—0
•outClkDivDown—2
9. Input the test voltage listed in Table 9 to channel 0 of the SCXI
module.
10. Call DAQ_Op. Set the following parameters:
•DAQdeviceNumber—The device number for the DAQ device
•channel—0
•gain—1 for a 16-bit E Series DAQ device
•count—100
•sampleRate—100
11. Call SCXI_Scale to convert the readings from binary to voltage.
Set the following parameters:
•SCXIChassisID—The device number assigned by MAX
•moduleSlot—1
•channel—0
•SCXIgain—The gain you are testing
•TBgain—1
•DAQboard—The device number for the DAQ device
•DAQChannel—0
•DAQgain—1
•numPoints—100
•binArray—The array returned from DAQ_Op
The result is a set of scaled voltages read from the SCXI module.
12. Average the results returned by SCXI_Scale. Compare the averaged
result to the upper and lower limits listed in Table 9.
13. Repeat steps 6 through 12 for each remaining test point.
14. Repeat steps 6 through 13 for each remaining channel, changing the
moduleChan variable to the channel number you are testing.
You have finished verifying the operation of the SCXI-1141/1142/1143.

SCXI-1141/1142/1143 Calibration Procedure 8 ni.com
Verifying Filter Parameters
Complete the following steps to set up the SCXI-1141/1142/1143 for this
verification process:
1. Read the Test Conditions section in this document.
2. Ensure that the E Series DAQ device is connected to the
SCXI-1141/1142/1143.
3. Call SCXI_Configure_Filter to enable the cutoff filter.
Set the following parameters:
•SCXIchassisID—The value obtained from MAX
•moduleSlot—1
•channel—0
•filterMode—1
•freq—10 kHz
•cutoffDivDown—0
•outClkDivDown—2
4. Call SCXI_Set_Gain to configure the module to a gain of 1.
Set the following parameters:
•SCXIchassisID—The value obtained from MAX
•moduleSlot—1
•moduleChan—0
•gain—1
5. Connect the calibrator to analog input channel 0. Refer to Table 7 to
determine which pins on the 96-pin front connector correspond to the
positive and negative inputs of the specified channel. If you are using
an SCXI-1304 connected to the SCXI-1141/1142/1143, connect the
calibrator to the AI 0 + and AI 0 – inputs.
6. Connect the DMM to the output of channel 0. Refer to Table 8 to
determine which pins on the 50-pin rear connector correspond to the
positive and negative outputs for the specified channel. For example,
the positive output for channel 0 is pin 3, which is AI 0 +. The negative
output for channel 0 is pin 4, which is AI 0 –.
Verifying Stopband Attenuation
Verify the stopband attenuation by performing the following steps:
1. Set the calibrator to output a 10 kHz, 1 Vrms sine wave.
2. With a DMM, ensure that you read a 1 Vrms signal.
3. Increase the input signal frequency generated by the calibrator until the
level read by the DMM is 10 mVrms.

©National Instruments Corporation 9 SCXI-1141/1142/1143 Calibration Procedure
4. Verify that the frequency is within the limits shown in Table 2.
Verifying Corner Frequency
Verify the corner frequency by performing the following steps:
1. Set the calibrator to output a 10 kHz, 1 Vrms sine wave.
2. Verify that the DMM output is within the values shown in Table 3.
Verifying Passband
Verify the passband by performing the following steps:
1. Set the calibrator output to a 1 Vrms sine wave at the frequency
specified in Tables 4, 5, or 6.
2. Verify that the DMM output is within the bounds specified by
Tables 4, 5, or 6.
3. Repeat steps 1 and 2 until all test points are verified.
Table 2. Input Frequency
Module Lower Limit (kHz) Upper Limit (kHz)
SCXI-1141 12.5 13.5
SCXI-1142 31.0 33.0
SCXI-1143 17.5 19.0
Table 3. SCXI-1141/1142/1143 Output
Module Lower Limit (Vrms)Upper Limit (Vrms)
SCXI-1141 0.9825 1.0201
SCXI-1142 0.6837 0.7331
SCXI-1143 0.6916 0.7765
Table 4. Passband Test Points for the SCXI-1141
Frequency (kHz) Lower Limit (Vrms)Upper Limit (Vrms)
5.94 0.9803 1.0143
9.39 0.9803 1.0143

SCXI-1141/1142/1143 Calibration Procedure 10 ni.com
Adjusting the SCXI-1141/1142/1143
This section contains three adjustment procedures: one for measuring gain
error, one for adjusting calibration gain constants, and one for adjusting
filter AC gain.
Measuring Gain Errors
Complete the following steps to measure the gain errors in the
SCXI-1141/1142/1143:
1. Read the Test Conditions section in this document.
2. Refer to Table 9 for the specifications to be tested. Table 9 shows all
acceptable settings for the module.
3. Ensure that the E Series DAQ device is connected to the
SCXI-1141/1142/1143.
4. Call SCXI_Single_Chan_Setup to configure the module for
single-channel measurements. Set the following parameters:
•SCXIchassisID—The value obtained from MAX
•moduleSlot—1
•moduleChan—0
•DAQdeviceNumber—The device number assigned by MAX
for the E Series DAQ device
5. Call SCXI_Set_Gain to configure the module to the gain value you
want to adjust. Set the following parameters:
•SCXIchassisID—The value obtained from MAX
•moduleSlot—1
•moduleChan—0
•gain—The gain value from Table 9 that you are currently testing
Table 5. Passband Test Points for the SCXI-1142
Frequency (kHz) Lower Limit (Vrms)Upper Limit (Vrms)
2.5 0.9596 0.9889
5.0 0.8909 0.9336
Table 6. Passband Test Point for the SCXI-1143
Frequency (kHz) Lower Limit (Vrms)Per Limit (Vrms)
5.0 0.9882 1.0119